This invention relates to a method of estimating the fuel/air ratio of a mixture supplied to an internal combustion engine and particularly to such a method for estimating the fuel/air ratio based on the measurement of the pressure in a cylinder of the engine during the combustion cycle of the cylinder.
In order to obtain the performance and emission objectives for an internal combustion engine, it is necessary to closely control the engine operating parameters. One such parameter is the fuel/air ratio of the fresh mixture delivered to the engine. In current practice, the fuel/air ratio is generally controlled by a closed loop control system in response to an exhaust gas O.sub.2 sensor to maintain a desired fuel/air ratio. While O.sub.2 sensors provide accurate estimates of the fuel/air ratio, their use in a closed loop control system with the transportation lag inherent in the system results in a sluggish response.
In view of the foregoing, it would be desirable to use the information from a cycle to cycle estimation of the fuel/air ratio to effectively regulate the fuel/air ratio at any desired (including the stoichiometric) value. In accord with this invention such information is obtained from the in-cylinder pressure transducers which have also proved to be highly effective in both detonation detection and spark timing control.